New Mexico Geological Society Annual Spring Meeting — Abstracts

Cerro Colorado is a 2.5-2.6 Ma dissected cinder cone in the Cerros del Rio volcanic field, west of Santa Fe, NM. The volcano stands 2225 m high and includes a well-defined 325 m diameter central vent characterized by inward dipping beds of moderately to strongly welded and highly oxidized scoria deposits and effusive lava flows. These transition sharply to periclinally dipping wall facies composed of vesiculated fragments, oxidized and unoxidized cinders, spatter agglutinate, and lava flows. While Cerro Colorado units follow general cinder cone facies patterns (central crater facies, proximal and distal wall facies) and granularity trends (decreasing cinder size away from summit), exposed sections deviate from the idealized cinder cone models. Several wall facies outcrops show multiple and regular alternations between explosive (pyroclastic falls) and effusive (lava flows) cycles. Pyroclastic deposits are highly vesiculated while lava flows are noticeably non-vesicular. These observations indicate that Cerro Colorado eruptions fluctuated from undegassed to degassed events, implying the existence of a shallow magma storage reservoir and challenging the simple feeder-dike plumbing system cinder cone model.

Paleomagnetic data along with physical volcanology observations (volcanic facies distribution, vesicle size and amount; degree of fragmentation) and petrology data (presence of hydrous phases, SiO₂ wt. %, and degree of fractionation) are being collected to characterize and compare the emplacement and timing of effusive versus extrusive units and the formation and deformation of the volcano edifice. Preliminary rock magnetic data indicate the presence of single domain and pseudo single domain Fe-Ti oxide phases; medium-Ti titanomagnetite is the principal magnetic phase carrying both the remanence and anisotropy. The presence of Fe₇S₈ suggests a low temperature magmatic source. The entirety of the dataset will be used to track the degassing, crystallization, and compositional evolution of the Cerro Colorado system over time providing new insight into cinder cone system dynamics.

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